Field of the Invention
The present invention relates to an imaging apparatus, a control method of the imaging apparatus, a program for performing the control method, and a storage medium of storing the program.
Description of the Related Art
There has been proposed an imaging apparatus which is equipped with, as the driving source of a camera mechanical part and a lens, an actuator which causes elliptic motion at a predetermined position of a vibrator such that the vibrator and a friction member frictionally in contact with the vibrator relatively move.
In the vibrator which constitutes the actuator, for example, a piezoelectric element serving as an electro-mechanical energy converting element is bonded to an elastic body such as metal or the like, and two-phase AC (alternate current) voltages having mutually different phases can be applied to the piezoelectric element. Thus, vibration waves are excited on the surface of the vibrator by applying the voltages to the piezoelectric element, and the vibrator is relatively moved by pressurizing it against the friction member, so that the vibrator slides on the surface of the friction member with desired driving force.
When the vibrator is being pressurized and in contact with the surface of the friction member, friction force generates. Thus, the actuator remains and is held at its initial position even after the voltage application is terminated. Accordingly, the friction force like this is also called holding force.
However, when the vibrator is held at the same position on the surface of the friction member for a long time, a small amount of water (or moisture) in the air coheres at the contact portion between the vibrator and the friction member, so that the friction force, i.e., the holding force, decreases. Then, when the vibrator is pressurized (or pressed) by external force in the state that the holding force has decreased, there is a case where the actuator inevitably moves. When the actuator for driving the lens moves, an out of focus occurs.
In this context, the driving apparatus for recovering decreased holding force has been proposed (Japanese Patent No. 5110824). When a vibrational wave motor stops for a predetermined time, this driving apparatus drives the vibrator to evaporate water or moisture by frictional heat generated between the vibrator and the rotation member, thereby recovering the torque of the motor.
Incidentally, when the imaging apparatus is used in a high-humidity environment, or when dew condensation (or dewfall) occurs due to movement of the imaging apparatus from a low-temperature environment to a high-temperature environment, water easily coheres at the contact portion as compared with a case where the imaging apparatus is used in a normal-temperature environment. For this reason, the out of focus occurs more easily in the imaging apparatus when it is used in the high-humidity environment.
An object of the present invention is to provide an imaging apparatus capable of maintaining good performance even if it is used in the high-humidity environment.